Method of fabricating an organic light emitting display device

ABSTRACT

An organic light emitting display device and a method of fabricating the same. A dummy pattern is formed in an emission region to increase the step height of the emission region by an electrode material while a thin film transistor is fabricated, so that a distance between a pixel electrode and a donor film is decreased during fabrication of an organic layer. This reduced distance reduces laser energy for transfer using laser-induced thermal imaging, thus improving life span and efficiency of the device. Further, the pixel electrode can extend into a thin film transistor region and a capacitor region, thus enhancing an aperture ratio.

CLAIM OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION

This application makes reference to, incorporates the same herein, andclaims all benefits accruing under 35 U.S.C. §119 from an applicationearlier filed in the Korean Intellectual Property Office on 13 Dec. 2004and there duly assigned Serial No. 10-2004-0105146. Furthermore, thisapplication is a divisional of Applicants' Ser. No. 11/297,343 filed inthe U.S. Patent & Trademark Office on 9 Dec. 2005, and assigned to theassignee of the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting displaydevice and a method of fabricating the same, and more particularly, toan organic light emitting display device with a pixel region having anincreased step difference to facilitate the deposition of an organiclayer using a laser-induced thermal imaging method.

2. Description of the Related Art

Among flat panel display devices, an organic light emitting displaydevice has a fast response time shorter than 1 ms, consumes littlepower, and has a wide viewing angle range because it can emit light byitself. As a result, the organic light emitting display device has theadvantage of a moving picture displaying medium regardless of the sizethereof. Further, the organic light emitting display device can befabricated at a low temperature, and its fabricating process is simplebased on the existing semiconductor processing technology, thusattracting attention as a next generation flat panel display device.

According to materials and processes, the organic light emitting displaydevice can be widely classified into a polymer device using a wetprocess, and a small molecule device using a deposition process. As amethod for patterning a polymer or small molecule emission layer, aninkjet printing method is applied using limited materials for organiclayers except for the emission layer, and has a complicated structure tobe applied to a substrate. Further, a metal mask is needed to patternthe emission layer by the deposition process, so that there is muchtrouble in fabricating a large-sized device.

Meanwhile, a laser-induced thermal imaging (LITI) method has beenrecently developed as an alternative to the foregoing patterning method.The laser-induced thermal imaging method converts laser light from alight source into heat energy, and uses the heat energy to transfer apattern forming material to an objective substrate, thus forming apattern on the substrate. In the laser-induced thermal imaging method, adonor substrate formed with a transfer layer, a light source and anobjective substrate are needed. Further, in the laser-induced thermalimaging method, the donor substrate and the objective substrate arelaminated so that the donor substrate is adhered to the highest portionof the objective substrate.

However, in typical LITI processes for forming an organic light emittingdisplay device, a large gap exists between the donor substrate and thepixel electrode. This large gap requires more laser energy for the LITIprocess, leading to damage and deterioration of the organic emissionlayer. Therefore, what is needed is an improved structure where thislarge gap is not apt to occur.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved design for an organic light emitting display device and animproved method of making the same.

It is further an object of the present invention to provide an improveddesign and method of making that reduces the gap in the LITI process.

These and other objects can be achieved by an organic light emittingdisplay device and a method of fabricating the same, in which a dummypattern is provided under a pixel electrode of an emission region, sothat a distance between a donor substrate and the pixel electrode isminimized, thus enhancing the efficiency of laser energy in a LITIprocess, and improving the life span and efficiency of an organic layer.

In an exemplary embodiment of the present invention, an organic lightemitting display device includes an emission region including a pixelelectrode, an organic layer that includes at least an emission layer,and an opposite electrode on a substrate, the emission region beingdefined by a pixel defining layer, a dummy pattern being arranged in theemission region under the pixel electrode, a thin film transistor regionincluding a gate electrode and source and drain electrodes, and acapacitor region including a lower electrode and an upper electrode.

In another exemplary embodiment of the present invention, a method offabricating an organic light emitting display device includes formingfirst conductive layer patterns on a substrate that is divided into afirst region, a second region and a third region, respectively, forminga first insulating layer on the substrate and on the first conductivelayer patterns, forming second conductive layer patterns on the firstinsulating layer in the first region, the second region and the thirdregion, respectively, forming a second insulating layer on an entiresurface of the second conductive layer and on exposed portions of thefirst insulating layer, forming third conductive layer patterns on thesecond insulating layer in first region, the second region and the thirdregion, respectively, forming a third insulating layer on an entiresurface of the third conductive layer and on exposed portions of thesecond insulating layer, forming a pixel electrode on the thirdinsulating layer in the first region, the pixel electrode adapted to beconnected to the third conductive pattern in the second region, forminga fourth insulating layer on the pixel electrode and on exposed portionsof the third insulating layer, patterning the fourth insulating layer toexpose at least a portion of the pixel electrode in the first region,forming an organic layer on the exposed portion of the pixel electrode,the organic layer including at least an emission layer and forming anopposite electrode on at least the organic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a cross-sectional view of a method of making an organic lightemitting display device;

FIG. 2 is a cross-sectional view of a method of making an organic lightemitting display device according to an embodiment of the presentinvention; and

FIG. 3 is a view of a finished organic light emitting display deviceproduced by the method of FIG. 2 according to the principles of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

A method of fabricating an organic light emitting display device will bedescribed in conjunction with FIG. 1. FIG. 1 is a cross-sectional viewof an organic light emitting display device, which includes an emissionregion I, a thin film transistor region II, and a capacitor region III.

To begin, a buffer layer 110 is formed on a substrate 100. Preferably,the buffer layer 110 is used to prevent impurities in the substrate 100from migrating into the device formed in a subsequent process.Subsequently, an amorphous silicon layer (not shown) is formed as asemiconductor layer having a predetermined thickness on the buffer layer110. Then, the amorphous silicon layer is crystallized by excimer laserannealing (ELA), sequential lateral solidification (SLS), metal inducedcrystallization (MIC), metal induced lateral crystallization (MILC), orthe like. The crystallized silicon layer is patterned by aphotolithography process, thus forming a polysilicon layer pattern 120in the thin film transistor region II of a unit pixel. At this time, thepolysilicon layer pattern can be additionally formed as a capacitorelectrode in the capacitor region III.

Next, a gate insulating layer 130 is formed on the entire surface of theresultant structure. At this time, the gate insulating layer 130 can beformed of a silicon oxide (SiO₂) layer, a silicon nitride (SiN_(x)) or alaminated layer thereof.

Then, the polysilicon layer pattern 120 of the thin film transistorregion II is doped with impurities. At this time, source and drainregions 126 and 124 are formed in the thin film transistor region II.Further, a channel region 122 is formed between the source and drainregions 126 and 124.

Then, a conductive layer (not shown) for a gate electrode is formed onthe entire surface of the resultant structure. The conductive layer forthe gate electrode is formed of a single layer of molybdenum (Mo) or analloy such as molybdenum-tungsten (MoW), a single layer of aluminum (Al)or an alloy such as aluminum-neodymium (Al—Nd), or a double layer of theabove-mentioned metals.

Then, the conductive layer for the gate electrode is etched byphotolithography and etching processes, thus forming a gate electrode132 in the thin film transistor region II and a lower electrode 134 inthe capacitor region III, respectively. In the case where the thin filmtransistor is an n-channel metal oxide semiconductor (NMOS), impurityions can be lightly doped using the gate electrode 132 as an ionimplantation mask, thus forming a lightly-doped drain (LDD) region (notshown).

Then, an interlayer insulating layer 140 is formed on the entire surfaceof the resultant structure. Subsequently, the interlayer insulatinglayer 140 and the gate insulating layer 130 are etched byphotolithography and etching processes, thus forming a contact hole forexposing the source and drain regions 126 and 124.

Then, a material for forming source and drain electrodes is formed onthe interlayer insulating layer 140. The source and drain electrodematerial is etched by photolithography and etching processes, thusforming source and drain electrodes 150 and 152 in the thin filmtransistor 7 region II and an upper electrode 154 in the capacitorregion III, respectively. Here, the source and drain electrodes 150 and152 are connected to the source and drain regions 124 and 126respectively.

Then, a passivation layer 160 and a planarization layer 170 are formedon the entire surface of the resultant structure. Then, theplanarization layer 170 and the passivation layer 160 are etched byphotolithography and etching processes, thus forming a via contact holeto expose one of the source and drain electrodes 150 and 152. In FIG. 1,the drain electrode 152 and not the source electrode 150 is shown to beexposed by the via contact hole.

A pixel electrode 180 is then formed to be connected to the drainelectrode 152 through the via contact hole. At this time, the pixelelectrode 180 is formed as a reflective electrode. Then, a pixeldefining layer 190 is formed on the entire surface of the resultantstructure, and is patterned to expose a portion of the pixel electrode180 in emission region I.

Then, an organic layer (not shown) including at least the emission layeris formed on the pixel electrode 180. The organic layer is formed by anLITI method using the donor substrate that includes base substrate 200,a light-to-heat conversion layer 210 and a transfer layer 220. Then, anopposite electrode (not shown) is formed, and an encapsulating processis performed, thus completing the organic light emitting display deviceof FIG. 1.

In the organic light emitting display device of FIG. 1, the thin filmtransistor region II and the capacitor region III are formed to be lowerthan the emission region I. In other words, the thin film transistorregion II and the capacitor region III are different in height by themetal electrodes, the gate electrode 132, the source and drainelectrodes 150 and 152, the lower electrode 134 and the upper electrode154, which are laminated in the thin film transistor region II and thecapacitor region III but not in the emission region I.

The step difference manifests itself at interconnections around the unitpixel and a peripheral portion thereof. For example, the thickness of adata line causes a data line region to be relatively higher than theemission region I. Such a structure can cause some problems in the LITIprocess for forming the organic layer. As the height T1 for detachingthe emission region I and the transfer layer 220 from the donorsubstrate becomes larger, laser energy needed for transfer increases. Ahigh laser energy is likely to damage the emission layer of the organiclight emitting display device. Thus, the efficiency and life span of theresultant organic light emitting display device are decreased.

Turning now to FIGS. 2 and 3, FIG. 2 is a cross-sectional view of amethod of making an organic light emitting display device according toan embodiment of the present invention and FIG. 3 is the finishedorganic light emitting display device made according to the method ofFIG. 2. As illustrated in FIGS. 2 and 3, the organic light emittingdisplay device is divided into an emission region I, a thin filmtransistor region II, and a capacitor region III for convenience.

Referring to FIG. 2, a first dummy pattern 328 formed of a polysiliconlayer, a second dummy pattern 336 formed of a gate electrode material,and a third dummy pattern 356 formed of a material for forming sourceand drain electrodes are laminated in the emission region I of asubstrate 300, and a pixel electrode 380 is formed above the dummypatterns. Further, a thin film transistor including a gate electrode 332and source and drain electrodes 350 and 352 are formed in the thin filmtransistor region II of the substrate 300. Also, a first capacitorincludes a first electrode 329 formed of a poly silicon layer pattern, asecond electrode 334 formed of a gate electrode material, and a gateinsulating layer 330 between the first and second electrodes 329 and334. And, a second capacitor includes a third electrode 354 made of thesource and drain electrode material, and an interlayer insulating layer340 between the second electrode 334 and the third electrode 354 andlocated in the capacitor region III. To form an organic layer (referencenumeral 430 in FIG. 3) in the emission region I by a LITI method, adonor substrate including a base substrate 400, a light-to-heatconversion layer 410 and a transfer layer 420 are arranged and laminatedon the substrate 300.

As shown in FIG. 2, the first dummy pattern 328, the second dummypattern 336 and the third dummy pattern 356 are laminated in theemission region I, but the present invention is not limited thereto.Alternatively, two or more patterns among the dummy patterns can belaminated. Here, the pixel electrode 380 can be formed of a reflectiveelectrode or a laminated layer including a reflective electrode so thatthe organic light emitting display device is a top emission type. Thepixel electrode 380 can extend into the thin film transistor region IIand the capacitor region III, thus enlarging an aperture ratio. Further,the double capacitor structure in the capacitor region III can bereplaced by a single capacitor structure including the second electrode334 and the third electrode 354.

Meanwhile, a pixel defining layer 390 defining the emission region isformed on the pixel electrode 380. Here, the pixel defining layer 390 isformed to a thickness of 3,000 Å or less. Preferably, a distance T2between the transfer layer 420 of the donor substrate and the pixelelectrode 380 is 3,000 Å or less. Even though the emission region I, thethin film transistor region II and the capacitor region III have thesame step difference, the transfer layer 420 and the pixel electrode 380are spaced apart from each other by a distance as much as the thicknessof the pixel defining layer 390.

A method of fabricating the organic light emitting display of FIG. 2according to an embodiment of the present invention will now bedescribed. A buffer layer 310 is formed on the substrate 300 includingin the emission region I, in the thin film transistor region II and inthe capacitor region Ill. The buffer layer 310 is formed to preventimpurities in the substrate 300 from migrating into the device formedabove in a subsequent process.

Subsequently, an amorphous silicon layer (not shown) is formed as asemiconductor layer having a predetermined thickness on the buffer layer310. Then, the amorphous silicon layer is crystallized by excimer laserannealing (ELA), sequential lateral solidification (SLS), metal inducedcrystallization (MIC), metal induced lateral crystallization (MILC), orthe like. The crystallized silicon layer is patterned by aphotolithography process, thus forming the first dummy pattern 328, thepolysilicon layer pattern 320 and the first electrode 329 in theemission region I, the thin film transistor region II and the capacitorregion III, respectively.

Then, a gate insulating layer 330 is formed on the entire surface of theresultant structure. At this time, the gate insulating layer 330 can beformed of a silicon oxide (SiO₂) layer, a silicon nitride (SiN_(x)) or alaminated layer thereof.

Then, the polysilicon layer pattern 320 in the thin film transistorregion II and in the first electrode 329 of the capacitor region III aredoped with impurities on the gate insulating layer 330. At this time,source and drain regions 326 and 324 are formed in the thin filmtransistor region II. Further, a channel region 322 is formed betweenthe source and drain regions 326 and 324.

Then, a conductive layer (not shown) for a gate electrode is formed onthe entire surface of the resultant structure. The conductive layer forthe gate electrode is formed of a single layer of molybdenum (Mo) or analloy such as molybdenum-tungsten (MoW), a single layer of aluminum (Al)or an alloy such as aluminum-neodymium (Al—Nd), or a double layer of theabove-mentioned metals. Then, the conductive layer for the gateelectrode is etched by photolithography and etching processes, thusforming the second dummy pattern 336, the gate electrode 332 and thesecond electrode 334 in the emission region I, the thin film transistorregion II and the capacitor region III, respectively. In the case wherea thin film transistor is an n-channel metal oxide semiconductor (NMOS),impurity ions can be lightly doped using the gate electrode 332 as anion implantation mask, thus forming a lightly-doped drain (LDD) region(not shown).

Then, an interlayer insulating layer 340 is formed on the entire surfaceof the resultant structure. Subsequently, the interlayer insulatinglayer 340 and the gate insulating layer 330 are etched byphotolithography and etching processes, thus forming a contact hole forexposing the source and drain regions 326 and 324. Then, a material forforming source and drain electrodes is formed on the interlayerinsulating layer 340.

Then, the source and drain electrode material is etched byphotolithography and etching processes, thus forming the third dummypattern 356, the source and drain electrodes 350 and 352 and the thirdelectrode 354 in the emission region I, the thin film transistor regionII and the capacitor region III, respectively. Here, the source anddrain electrodes 350 and 352 are connected to the source and drainregions 326 and 324.

Next, a passivation layer 360 and a planarization layer 370 are formedon the entire surface of the resultant structure. Then, theplanarization layer 370 and the passivation layer 360 are etched byphotolithography and etching processes, thus forming a via contact holewhich exposes one of the source and drain electrodes 350 and 352. InFIG. 2, the drain electrode 352 and not the source electrode 350 isshown to be exposed by the via contact hole.

Then, a pixel electrode 380 is formed to be connected to the drainelectrode 352 through the via contact hole. At this time, the pixelelectrode 380 is made of a reflective material. Here, the pixelelectrode 380 can be formed of a single layer of the reflective materialor a laminated layer that includes a reflective electrode. The singlelayer of the reflective electrode can include Ag or an Ag alloy. Thelaminated layer can include a structure oftransparent/reflective/transparent electrodes or reflective/transparentelectrodes, wherein the reflective electrode can include Ag or an Agalloy, and the transparent electrode can include indium tin oxide (ITO),indium zinc oxide (IZO) or In₂O₃. Because the reflective electrode isemployed as the pixel electrode 380, the pixel electrode 380 can beprovided only in the emission region I. Alternatively, the pixelelectrode 380 can extend into the thin film transistor region II and thecapacitor region III.

Then, a pixel defining layer 390 is formed on the entire surface of theresultant structure, thus exposing a portion of the pixel electrode 380in the emission region I. At this time, the pixel defining layer 390 isformed to a thickness of 3,000 Å or less in the emission region I tothus facilitate the following organic layer forming process.

Then, an organic layer (reference numeral 430 in FIG. 3) including atleast the emission layer is formed on the pixel electrode 380. Further,the organic layer can further include at least one layer among a holeinjection layer, a hole transporting layer, an electron transportinglayer, and an electron injection layer. Also, the organic layer can beformed by an LITI method.

The LITI method is performed as follows. The substrate 300 is disposedopposite to the donor substrate that includes the base substrate 400,the light-to-heat conversion layer 410 and the transfer layer 420, andthen arranged and laminated. Radiation from a laser is applied to thebase substrate 400 of the laminated donor substrate, thus transferringthe transfer layer 420 under the light-to-heat conversion layer 410 tothe exposed portion of the pixel electrode 380 on substrate 300.Preferably, the distance T2 between the transfer layer 420 of the donorsubstrate and the pixel electrode 380 is 3,000 Å or less, allowing forless laser energy needed for transferring the transfer layer 420. Then,an opposite electrode 440 is formed over the transferred structure andan encapsulation process is performed, thus completing the organic lightemitting display device.

Turning now to FIG. 3, FIG. 3 is a view of the finished organic lightemitting display produced by the method of FIG. 2. As illustrated inFIG. 3, the organic layer 430 is arranged on top of the pixel defininglayer 390 and on top of the previously exposed portion of pixelelectrode 380. The organic layer was previously the transfer layer 420of FIG. 2. The organic layer 430 contains an emission layer and can alsoinclude one or more of a hole injection layer, a hole transportinglayer, an electron transporting layer and an electron injection layer.On top of the organic layer 430 is the opposite electrode 440.

As illustrated in FIG. 3, the final product does not have a perfectlyflat top surface but instead contains relief (or differences in height)across the top surface caused by the aperture that once exposed aportion of the pixel electrode 380 as well as the valley formed betweenthe capacitor region and the thin film transistor region.

As described above, according to the present invention, the dummypattern is formed under the pixel electrode of the emission region so asto increase the step difference, and thus minimize the distance betweenthe pixel electrode and the donor substrate when the organic layer isformed, thus minimizing the laser energy needed for the transfer, andenhancing the efficiency of the laser energy during the LITI process. Asthe laser energy is minimized, the life span and efficiency of theemission layer are improved. Further, the pixel electrode can extend tothe thin film transistor region and the capacitor region, thus improvingan aperture ratio.

Although the present invention has been described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that a variety of modifications and variations can bemade to the present invention without departing from the spirit andscope of the present invention.

1-6. (canceled)
 7. A method of fabricating an organic light emittingdisplay device, comprising: forming first conductive layer patterns on asubstrate that is divided into a first region, a second region and athird region, respectively; forming a first insulating layer on thesubstrate and on the first conductive layer patterns; forming secondconductive layer patterns on the first insulating layer in the firstregion, the second region and the third region, respectively; forming asecond insulating layer on an entire surface of the second conductivelayer and on exposed portions of the first insulating layer; formingthird conductive layer patterns on the second insulating layer in firstregion, the second region and the third region, respectively; forming athird insulating layer on an entire surface of the third conductivelayer and on exposed portions of the second insulating layer; forming apixel electrode on the third insulating layer in the first region, thepixel electrode adapted to be connected to the third conductive patternin the second region; forming a fourth insulating layer on the pixelelectrode and on exposed portions of the third insulating layer;patterning the fourth insulating layer to expose at least a portion ofthe pixel electrode in the first region; forming an organic layer on theexposed portion of the pixel electrode, the organic layer including atleast an emission layer; and forming an opposite electrode on at leastthe organic layer.
 8. The method of claim 7, wherein the first region isan emission region, the second region is a thin film transistor region,and the third region is a capacitor region.
 9. The method of claim 7,wherein the first conductive layer patterns include a first dummypattern, a polysilicon layer pattern including a channel region andsource and drain regions, and a first electrode of a capacitor.
 10. Themethod of claim 7, wherein the first insulating layer is a gateinsulating layer.
 11. The method of claim 7, wherein the secondconductive layer patterns include a second dummy pattern, a gateelectrode, and a second electrode of a capacitor.
 12. The method ofclaim 7, wherein the second insulating layer is an interlayer insulatinglayer.
 13. The method of claim 7, wherein the third conductive layerpatterns include a third dummy pattern, source and drain electrodes, anda third electrode of a capacitor.
 14. The method of claim 7, wherein thethird insulating layer includes either a passivation layer and aplanarization layer or a laminated layer of the passivation layer andthe planarization layer.
 15. The method of claim 7, wherein the pixelelectrode comprises reflective material.
 16. The method of claim 7,wherein the pixel electrode is formed throughout the first region, thesecond region and the third region.
 17. The method of claim 7, whereinthe patterned fourth insulating layer is a pixel defining layer.
 18. Themethod of claim 7, wherein the patterned fourth insulating layer has athickness of 3,000 Å or less.
 19. The method of claim 7, wherein theorganic layer further includes at least one thin layer selected from agroup consisting of a hole injection layer, a hole transporting layer,an electron transporting layer and an electron injection layer.
 20. Themethod of claim 7, wherein the organic layer is produced by alaser-induced thermal imaging (LITI) process.